1. Field of the Invention
The present invention relates to a semiconductor device capable of input and output of information by using electromagnetic waves. It is to be noted that the semiconductor device in this specification refers to all devices that can function by utilizing semiconductor characteristics, and electro-optic devices, semiconductor circuits, and electrical appliances, which have this function, are all semiconductor devices.
2. Description of the Related Art
In recent years, wireless chips for RFID (radio frequency identification system) have been researched and put into practical use as an information and communication technology utilizing electromagnetic waves.
RFID refers to a communication technology over electromagnetic waves between a reader/writer and a semiconductor device capable of wirelessly transmitting and receiving information (also called an RFID tag, an RF tag, an ID tag, an IC tag, a wireless tag, an electronic tag, a wireless chip, or an ID chip), so that data can be stored in or read out from the semiconductor device. Such a semiconductor device includes an antenna and an integrated circuit having a signal processing circuit provided with a memory circuit and the like.
A wireless chip used for RFID obtains an operating power by electromagnetic induction from electric waves that are received with a reader/writer, and exchanges data with the reader/writer by utilizing the electric waves. A wireless chip, in general, has an antenna which transmits and receives such electric waves and which is formed separately from an integrated circuit and connected to the integrated circuit.
In the case where an antenna and an integrated circuit are thus formed separately from each other and connected to each other, the both need to be electrically connected, which leads to low yield because of technical difficulty in connection between the antenna and a minute terminal of the integrated circuit. Moreover, stress applied at a connection point in the use of a wireless chip causes disconnection or poor connection. In particular, when a wireless chip is flexible, it is expected that poor connection is more likely to occur.
In order to solve the aforementioned problem of poor connection between an antenna and an integrated circuit, a wireless chip having an antenna coil formed over the same substrate has been suggested. For example, in a suggested wireless chip having an integrated circuit and an antenna coil formed over the same substrate, a conductor of the antenna coil is formed by a metal sputtering layer or a metal evaporation layer and by a copper plating layer formed over the metal sputtering layer or the metal evaporation layer. The metal sputtering layer and the metal evaporation layer include one of aluminum, nickel, copper, or chromium, or include an alloy of at least two of these metals (see Patent Document 1: Japanese Published Patent Application No. 2002-324890).
Accordingly, the conductor of the antenna coil has a stacked-layer structure of the metal sputtering layer or the metal evaporation layer, and the copper plating layer having lower electric resistance than the metal sputtering layer or the metal evaporation layer. Therefore, the loss of electromagnetic energy can be reduced as compared with a structure of only the metal sputtering layer or the metal evaporation layer, and communication distance to a reader/writer can be extended.
However, the present inventors found that the aforementioned conventional structure causes copper diffusion such as electromigration or stress migration, which adversely affects electrical characteristics of circuit elements in the integrated circuit formed over the same substrate as the antenna coil.